Hereinafter, a device to device communication environment will be described.
Device to device (D2D) communication refers to communication between an electronic device and another electronic device. In a broad sense, D2D communication refers to wire or wireless communication between electronic devices or communication between a machine and a device controlled by a person. However, it is general that D2D communication recently refers to wireless communication between electronic devices, i.e., devices performed without control of a person.
In the early 1990s when D2D communication has been introduced, D2D communication has been recognized as remote control or telematics and D2D communication markets have been very restrictive. However, D2D communication markets have received attention all over the world since D2D communication had been able to grow rapidly for last several years. Particularly, D2D communication has exerted its great influence at point of sales (POS) and security related application markets in the fields of fleet management, remote monitoring of machine and facilities, measurement of working time on construction machine facilities, and smart meter automatically measuring heat or the use of electricity. It is expected that D2D communication will be used for various purpose of uses in association with the existing mobile communication and low power communication solutions such as wireless high-speed Internet, Wi-Fi, and Zigbee and that its coverage will be extended to business to consumer (B2C) markets without limitation to business to business (B2B) markets.
In the D2D communication age, since all machines provided with a subscriber identity module (SIM) card may be able to perform data transmission and reception, they may remotely be controlled. For example, D2D communication technologies may be used for many machines and equipments such as cars, trucks, trains, containers, vending machines, and gas tanks. In this way, application ranges of D2D communication technologies are very broad.
According to the related art, since it was general that a user equipment was controlled separately, communication between a base station and a user equipment has been performed by a one-to-one communication mode. Supposing that many D2D devices perform communication with a base station through such a one-to-one communication mode, network overload will be caused by signaling generated between each of the D2D devices and the base station. As described above, if D2D communication is rapidly spread and widely used, a problem may occur due to overhead caused by communication between D2D devices or between each of the D2D devices and the base station.
Also, according to the related art, although studies for D2D direct communication have been made, studies for a method for performing seamless communication if a status of D2D connection is not good or switching (that is, handover or routing) of a communication mode between D2D and cellular network in D2D communication have been insufficient.